Chemical and biological separations are routinely performed in various industrial and academic settings to determine the presence and/or quantity of individual species in complex sample mixtures. There exist various techniques for performing such separations.
One particularly useful analytical process is chromatography combined with mass spectroscopy, which encompasses a number of methods that are used for separating ions or molecules for analysis. Liquid chromatography (‘LC’) is a physical method of separation wherein a liquid ‘mobile phase’ carries a sample containing one or more compounds for analysis (analytes) through a separation medium or ‘stationary phase.’ Liquid output by the LC device is nebulized to form droplets comprising the mobile phase and the analytes. Ideally, the mobile phase is removed, leaving the analytes. The analytes are provided to an ion source of a mass spectrometer (MS). Charged analytes are then provided to a mass analyzer for spectroscopic analysis.
Unfortunately, in known MS devices, among other problems, the percentage of analytes output from the LC column that are incident on a detector of the MS is comparatively small. For example, ionization can be incomplete, leaving the analytes only partially ionized. Furthermore, electrically-neutral analytes are not detected by the detector of the MS. Moreover, repulsion of analyte ions due to known space charge repulsion causes rarefaction. Decreased sample density translates to a comparatively small fraction of the sample ions entering the MS and, hence, reaching a detector in the MS. Ultimately, due to one or more of the noted factors, the overall efficiency of known MS devices is comparatively low.
What is needed, therefore, is a method and apparatus for providing analytes from an LC column to a mass analyzer that overcomes at least the drawbacks of known devices and methods described above.